import cv2
import numpy as np

img = cv2.imread('img/example.png')
h, w, c = img.shape

blue_img = img[:, :, 0: 1]
green_img = img[:, :, 1:2]
red_img = img[:, :, 2:]
black_channel = np.zeros((h, w, 1), dtype=img.dtype)
cv2.imshow('', black_channel)

blue = np.concatenate((blue_img, black_channel, black_channel), axis=2)
green = np.concatenate((black_channel, green_img, black_channel), axis=2)
red = np.concatenate((black_channel, black_channel, red_img), axis=2)

img = np.concatenate((blue_img, green_img, red_img), axis=2)

# cv2.imshow('', blue + green + red)
# cv2.imshow('', blue)
# cv2.imshow('', green)
# cv2.imshow('', red)

cv2.waitKey(0)